Just a moment ago, it seems, President Obama’s supporters were assailing the John Roberts Court for its supposed political activism. Now, Roberts has given Obamacare’s supporters their sweetest victory precisely because he did the political work that Obama and his allies wouldn’t, or couldn’t, do when they were enacting the health-care overhaul in 2010—calling the “mandate” undergirding the law what it actually is, a tax.

And Republicans, no longer able to question the law’s constitutionality (an issue deftly mooted by Roberts’s mandate-is-a-tax rationale), have rushed to take up the new line of attack suggested by Roberts. “The Supreme Court is confirming what we knew all along about this law,” said New Jersey Gov. Chris Christie, in a statement released moments after the court’s decision, “it is a tax on middle-class Americans.”

Grover Norquist, the antitax orthodoxy enforcer for the Republican Party, told The Daily Beast that the court’s ruling provided Republicans with an obvious course to victory in the fall. “The president was elected on a repeated commitment that he’d never raise taxes on anyone who earned less than $250,000 a year,” Norquist said. “He gets elected, he passes Obamacare, swearing that there’s no tax increase in it. OK. Between now and the election, we have a conversation about the fact that Obama lied his way into office, he said he wasn’t going to raise his taxes on lower-income people, and did.”

Florida Senator Marco Rubio, who, like Christie, is a potential Republican vice-presidential candidate, took up the theme on the Senate floor Thursday afternoon. “My friends, this is a middle-class tax increase,” Rubio said. “And millions of Americans now have an IRS problem.”

Mitt Romney, whose voice on the health-care issue is not fully trusted within his own party, once again vowed to undo the law partly modeled on his own reform in Massachusetts. “Obamacare was bad policy yesterday,” Romney said. “It’s bad policy today.”

Democrats, for their part, mostly expressed relief, and even some exuberance. But while House Minority Leader Nancy Pelosi may be inclined to spike the ball on the ruling, it would be surprising to see much of that from Obama himself. The president has scarcely mentioned his signature health-care law in his reelection campaign, not only because its constitutionality was in question, but because it remains, more than two years after passage, a very unpopular program. Polls on the eve of the Supreme Court’s decision showed that far more Americans opposed the Affordable Care Act than supported it, and nearly 70 percent wanted Washington to do little or nothing to replace it if the court overturned the law. Indeed, Obama seemed eager to move beyond the subject, saying he had no wish to “refight the political battles of two years ago or go back to the way things were.”

And while the Supreme Court’s decision will certainly animate the political right—Romney’s camp reports that money started flooding into its coffers within an hour of the ruling—the presumptive Republican nominee may be well advised against focusing too much on Obamacare. For one thing, voters have already spoken on the issue—and gave Republicans the House in 2010, when the ugly process of the law’s passage was still fresh in memory. But what has lifted the Romney campaign, and continues to dog the president, is the abiding national concern over a dreadful economy. Every moment that Romney spends talking about undoing Obamacare is a moment not spent on the subject that could bring him victory in the fall.